The ubiquitin-modifying enzyme A20 restricts the ubiquitination of RIPK3 and protects cells from necroptosis

A20 is an anti-inflammatory protein linked to multiple human diseases, however the mechanisms by which A20 prevents inflammatory disease are incompletely defined. We now find that A20 deficient T cells and fibroblasts are susceptible to caspase independent and RIPK3 dependent necroptosis. Global RIPK3 deficiency significantly rescues the survival of A20 deficient mice. A20 deficient cells exhibit exaggerated formation of RIPK1-RIPK3 complexes. RIPK3 undergoes physiological ubiquitination at lysine 5 (K5), and this ubiquitination event supports the formation of RIPK1-RIPK3 complexes. The catalytic cysteine of A20’s deubiquitinating motif is required for inhibiting RIPK3 ubiquitination and RIPK1-RIPK3 complex formation. These studies link A20 and RIPK3 ubiquitination to necroptotic cell death, and suggest new mechanisms by which A20 may prevent inflammatory disease. A20 is a deubiquitinating enzyme that inhibits NF-kB activation and restricts TNF-induced apoptosis1–4. A20 is a potent anti-inflammatory protein linked to multiple human autoimmune diseases and to human malignancies5, 6. Polymorphisms in the human TNFAIP3 gene (which encodes the A20 protein) are associated with reduced A20 function or expression that confer susceptibility to autoimmune diseases7, 8. Deletion of A20 in mice leads to widespread tissue inflammation and perinatal lethality2. A20 regulates multiple signaling cascades and as such, plays distinct physiological functions in different cell types5, 6. In myeloid cells, A20 prevents inflammation by restricting the activation of the Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use:http://www.nature.com/authors/editorial_policies/license.html#terms To whom correspondence should be addressed: University of California, San Francisco, 513 Parnassus Ave, S-1057, San Francisco, CA 94143-0451. [email protected]. *these authors contributed equally @Current address: Department of Gastroenterology and Hepatology, Tokyo Medical and Dental University, Tokyo, Japan HHS Public Access Author manuscript Nat Immunol. Author manuscript; available in PMC 2015 December 01. Published in final edited form as: Nat Immunol. 2015 June ; 16(6): 618–627. doi:10.1038/ni.3172. A uhor M anscript